# Ordered pairs.

Prior to understanding what is ordered pair let us know what is a pair first.

### What is a pair?

A pair is a set  which have only two elements. Like {a,b} , {me,my sister}. A pair can never have more than or less than two elements ; it always have exactly two elements.

### What is ordered pair?

A pair or set of two elements , in which order of its elements are predefined or the first element is always in first and second is always in second is known as an ordered pair.

An ordered pair having “a is its first element and “b” as its second element is denoted by:

{a,b}

### Equal ordered  pairs:

As , order of elements of an ordered pair is predefined ,

Two ordered pairs {a,b} and {c,d} are equal if and only if “a”=”c” and “b”=”d”

If “a” and “b” are not equal to “c” and “d” respectively the two ordered pairs cannot be equal.

### Note:

> A pair {a,b} is equal to another pair {b,a}

For example pairs {1,2}={2,1}

>An  ordered pair {a,b} is never equal to another ordered pair {b,a} unless a=b.

For example: order pairs {1,2} ≠ {2,1} but {1,1}={1,1}

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